The proposal's long-term objective is to understand economy of biological design and capacity matching in series biological pathways. By capacity matching is meant the question of whether successive steps in series (such as the enzymes in a reaction chain) have similar capacities, or whether one of those capacities is instead low and rate-limiting. The proposal's specific primary aim is to utilize the method of total parenteral nutrition (TPN) to test capacity matching between organs that process nutrients in series: the intestine, liver, circulation, and kidneys. A specific secondary aim is to utilize TPN to examine mechanisms of appetite satiation. The experiments utilize a new TPN model that administers an identical nutrient mix either by mouth or by TPN to rats.